EP 2 273 369 B1 discloses a method for displaying security-relevant information on a display device and a device for carrying out the method. The disclosed method comprises the step of entering at least one input value into a computing unit, the step of processing the input value with the help of computing in the computing unit to obtain an image-data sequence representing the input value, the step of forwarding the image-data sequence to a display device and the step of representing the image-data sequence on the display device, as well as the step of feeding the image data sequence into a check unit and the step of carrying out, by means of computing, a security check by generating a check code for the image data sequence, the step of comparing the check code with a plurality of comparison codes present in the check unit and the step of allocating the comparing code to be determined to a corresponding potential input value and comparing it to the input value in order to generate either a positive or a negative check result in the check unit in order to initiate a security-relevant reaction.
In this context, each comparing code corresponds to a pre-calculated CRC check sum based on a predetermined bitmap. This particularly means that for each possible bitmap, i.e. image data sequence, a valid CRC check sum is stored as a comparing code in the comparing unit.
A particular disadvantage of the disclosed method is that it works only if comparing codes corresponding to the entered values are stored in the check unit. If unknown input values are entered, this method will not work anymore. In addition, a minimal deviation of the entered input values, e.g. a different colour representation or another font size is sufficient in order to generate a check sum which differs from the stored check sum, resulting in an error report even if no error has occurred. Moreover, it has to be safeguarded when generating and storing the pre-calculated CRC check sums that these are correctly generated and stored.
EP 0 856 792 B1 discloses a method for safely representing an image on a monitor. In this context, two image memories which are independent from each other are provided, storing corresponding image data of an image to be displayed. Said image data are generated by means of an image processor and additionally stored in an image-retransmission buffer which drives the monitor. At specific points in time, the data from the individual memories are read out and compared to one another.
DE 43 32 143 A1 discloses a method for operating a data-display unit and units for carrying out the method. In analogy to patent specification EP 0 856 792 B1, two image memories are generated in this context wherein check sums are generated based on the data stored in the image memories. At specific points in time, these check sums are compared to one another.
The particular disadvantages of these two disclosed methods are that two image memories are required for carrying out the methods, thus requiring more material and increasing a complexity of a corresponding configuration.
EP 2 405 317 A1 discloses a method for safe parametrisation of a security device. The method comprises the steps of inserting a parameter value into a configuration unit by a user and displaying the parameter value on a display unit. The method further comprises the method steps of encrypting the parameter value in the configuration unit and of storing at least one feature resulting from the encryption. Upon verification by means of the feature, the parameter value is displayed on the display unit for a second time, the second display being timely and spatially correlated with the first display. The next step is a value comparison by the user of the parameter value represented by means of the two displays, and confirmation of a valid parameter indication if a correlation is determined. The next step is read-back-free reading out of validly entered parameter values from the configuration unit into the security device.
A disadvantage is that the verification of the entered and represented parameter values is exclusively carried out by means of visual examination on behalf of user.